In a Long Term Evolution (LTE) system, uplink power control is one of primary means to ensure a communication quality. Uplink power control can be performed to lower interference as much as possible between User Equipments (UEs) transmitting data over the same resource in adjacent cells and to ensure transmit power of the UEs to be used reasonably.
Uplink power to be controlled generally includes transmit power of a Physical Uplink Control Channel (PUCCH), transmit power of a Physical Uplink Shared Channel (PUSCH), transmit power of a Sounding Reference Signal (SRS) and transmit power of a Physical Random Access Channel (PRACH).
In the Long Term Evolution-Advanced (LTE-A) Release 10 (Rel-10), transmit power PPUCCH at which a UE transmits a PUCCH over a primary carrier is calculated in the equation of:
                    P        PUCCH            ⁡              (        i        )              =          min      ⁢                        {                                                                                                                P                                              CMAX                        ,                        c                                                              ⁡                                          (                      i                      )                                                        ,                                                                                                                          P                                          0                      ⁢                      _PUCCH                                                        +                                      PL                    c                                    +                                      h                    ⁡                                          (                                                                        n                          CQI                                                ,                                                  n                          HARQ                                                ,                                                  n                          SR                                                                    )                                                        +                                                            Δ                      F_PUCCH                                        ⁡                                          (                      F                      )                                                        +                                                            Δ                      TxD                                        ⁡                                          (                                              F                        ′                                            )                                                        +                                      g                    ⁡                                          (                      i                      )                                                                                                    ⁢                                          }                ⁢                                  [        dBm        ]              ,
Wherein: PCMAX,c(i) represents maximum allowable carrier transmit power configured for a carrier c in a sub-frame i. The parameter ΔF_PUCCH(F) is configured by a higher layer and corresponds to a power offset of a different PUCCH format relative to the PUCCH format 1a. ΔTxD(F′) represents a power offset of transmit diversity, and if the UE is configured to transmit via a two-antenna port, then ΔTxD(F′) is configured for the different PUCCH format by higher-layer signaling and takes its value in a set of {0, −2}dB; and if the UE is configured to transmit via a single-antenna port, then ΔTxD(F′)=0. h(ncQI, nHARQ, nSR) represents a power offset related to the number of bits carried on the PUCCH, wherein nCQI, represents the number of carried Channel State Information (CSI) bits, nHARQ represents the number of carried Acknowledgement (ACK)/NACK (Non-Acknowledgement) bits, and nSR represents the number of carried Scheduling Request (SR) bits. PO_PUCCH represents an expected target power value, of the PUCCH, configured by higher-layer signaling. g(i) represents a cumulative value of a power control command, and
            g      ⁡              (        i        )              =                  g        ⁡                  (                      i            -            1                    )                    +                        ∑                      m            =            0                                M            -            1                          ⁢                              δ            PUCCH                    ⁡                      (                          i              -                              k                m                                      )                                ,wherein δPUCCH represents a UE-specific revision value, also referred to a Transmit Power Control (TPC) command, δPUCCH(i−km) represents a revision value obtained in a sub-frame i−km, and for a Time Division Duplex (TDD) system, km represents the index of a downlink sub-frame in a set of downlink sub-frames for which an ACK/NACK feedback is needed in the current sub-frame, and M represents the number of downlink sub-frames in the set of downlink sub-frames, and for a Frequency Division Duplex (FDD) system, km=4 and M=1. PLc represents a path loss of the carrier c measured by the UE and can be measured by the UE, as configured by higher-layer signaling, over a pair of carriers or the primary carrier configured by information in the System Information Block 2.
In the LTE-A Rel-10, if a UE transmits no PUCCH over a carrier c in a sub-frame i, then transmit power PPUSCH,c(i) at which the UE transmits a PUSCH over the carrier c is calculated in the equation of:
                    P                  PUSCH          ,          c                    ⁡              (        i        )              =          min      ⁢                        {                                                                                                                P                                              CMAX                        ,                        c                                                              ⁡                                          (                      i                      )                                                        ,                                                                                                                          10                    ⁢                                                                  log                        10                                            ⁡                                              (                                                                              M                                                          PUSCH                              ,                              c                                                                                ⁡                                                      (                            i                            )                                                                          )                                                                              +                                                            P                                              O_PUSCH                        ,                        c                                                              ⁡                                          (                      j                      )                                                        +                                                                                    α                        c                                            ⁡                                              (                        j                        )                                                              ·                                          PL                      c                                                        +                                                            Δ                                              TF                        ,                        c                                                              ⁡                                          (                      i                      )                                                        +                                                            f                      c                                        ⁡                                          (                      i                      )                                                                                                    }                ⁢                                  [        dBm        ]              ,
In the LTE-A Rel-10, if a UE transmits a PUCCH over a carrier c in a sub-frame i, then transmit power PPUSCH,c(i) at which the UE transmits a PUSCH over the carrier c is calculated in the equation of:
                    P                  PUSCH          ,          c                    ⁡              (        i        )              =          min      ⁢                        {                                                                                          10                    ⁢                                                                  log                        10                                            ⁡                                              (                                                                                                                                            P                                ^                                                                                            CMAX                                ,                                c                                                                                      ⁡                                                          (                              i                              )                                                                                -                                                                                                                    P                                ^                                                            PUCCH                                                        ⁡                                                          (                              i                              )                                                                                                      )                                                                              ,                                                                                                                          10                    ⁢                                                                  log                        10                                            ⁡                                              (                                                                              M                                                          PUSCH                              ,                              c                                                                                ⁡                                                      (                            i                            )                                                                          )                                                                              +                                                            P                                              O_PUSCH                        ,                        c                                                              ⁡                                          (                      j                      )                                                        +                                                                                    α                        c                                            ⁡                                              (                        j                        )                                                              ·                                          PL                      c                                                        +                                                            Δ                                              TF                        ,                        c                                                              ⁡                                          (                      i                      )                                                        +                                                            f                      c                                        ⁡                                          (                      i                      )                                                                                                    }                ⁢                                  [        dBm        ]              ,
Wherein: {circumflex over (P)}CMAX,c(i) represents a linearity-domain value of PCMAX,c(i), i.e., {circumflex over (P)}CMAX,c(i)=10PCMAX,c(i)/10. {circumflex over (P)}PUCCH(i) represents a linearity-domain value of the PUCCH transmit power PPUCCH(i). MPUSCH,c(i) represents the size, in Resource Blocks (RBs), of a resource of the PUSCH over the carrier c. PO_PUSCH,c(j) represents an expected target power value of the PUSCH over the carrier c and is configured by higher-layer signaling. αc(j) represents a path loss compensation factor of the carrier c as a cell-specific parameter configured by higher-layer signaling. PLc represents a path loss of the carrier c measured by the UE and can be measured by the UE, as configured by higher-layer signaling, over a pair of carriers or a primary carrier configured by information in the System Information Block 2. With Ks=1.25, ΔTF,c(i)=10 log10((2BPRE-Ks−1)·βoffsetPUSCH) represents a different power offset corresponding to a different Modulation and Coding Scheme (MCS); and with Ks=0, ΔTF,c(i)=0 represents disablement of a function to adjust power according to an MCS, wherein Ks represents a UE-specific parameter indicated by higher-layer signaling. The Bits Per Resource Element (BPRE) represents the number of bits corresponding to each resource element on the PUSCH, and βoffsetPUSCH represents an offset of an encoding rate of uplink control information carried on the PUSCH relative to an encoding rate of uplink data on the PUSCH and is preconfigured by higher-layer signaling. fc(i) represents a PUSCH power control adjustment amount for which there are two patterns, i.e., a cumulative value and a current absolute value.
In the LTE-A Rel-10, transmit power PSRS at which the UE transmits an SRS over a carrier c is defined in the equation of:PSRS,c(i)=min{PCMAX,c(i),PSRS_OFFSET,c(m)+10 log10(MSRS,c)+PO_PUSCH,c(j)+αc(j)·PLc+fc(i)}[dBm],
Wherein PSRS_OFFSET,c(m) represents a power offset of the SRS, relative to a PUSCH, in a different antenna port configuration over the carrier c, m=0 corresponds to a periodic SRS, and m=1 corresponds to an aperiodic SRS. MSRS,c represents a transmit bandwidth, in RBs, of the SRS over the carrier c. The other parameters are the same as the power control parameters of the PUSCH over the carrier.
In the LTE-A Rel-10, transmit power at which a UE transmits a PRACH over a carrier c is defined in the equation of:PPRACH=min{PCMAX,c(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc}_[dBm],
Wherein PREAMBLE_RECEIVED_TARGET_POWER is calculated by a Media Access Control (MAC) layer of the UE as target power of the PRACH.
In the LTE-A Rel-10, an uplink power control scheme is based upon power control on concurrent transmission, in the same sub-frame, of a PDCCH and a PUSCH over the same or different carriers. If the total transmit power of a UE in the current sub-frame i exceeds the maximum transmit power allowed by the UE, then power shall be scaled down by the UE ensuring transmit power of the PUCCH preferentially while scaling down transmit power of the PUSCH over each carrier c with an equal proportion so as to satisfy the limited maximum transmit power allowed by the UE:
                    ∑        c            ⁢                        w          ⁡                      (            i            )                          ·                                            P              ^                                      PUSCH              ,              c                                ⁡                      (            i            )                                ≤          (                                                  P              ^                        CMAX                    ⁡                      (            i            )                          -                                            P              ^                        PUCCH                    ⁡                      (            i            )                              )        ,
Wherein {circumflex over (P)}PUSCH,c(i) represents a linearity-domain value of PPUSCH,c(i), and w(i) represents a power scaling down factor over each carrier with 0≦w(i)≦1. If no PUCCH is transmitted in the current sub-frame i, then {circumflex over (P)}PUCCH(i)=0.
If a UE transmits a PUSCH with Uplink Control Information (UCI) and a PUSCH without UCI concurrently in the current sub-frame i, and the total transmit power of the UE exceeds the maximum transmit power allowed by the UE, then the UE shall ensure firstly the transmit power of the PUCCH not to be scaled down and secondly the transmit power of the PUCCH with the UCI not to be scaled down while scaling down transmit power of the PUSCH over each carrier with an equal proportion so as to satisfy the limited maximum transmit power allowed by the UE:
                              P          ^                          PUSCH          ,          j                    ⁡              (        i        )              =          min      ⁡              (                                                            P                ^                                            PUSCH                ,                j                                      ⁡                          (              i              )                                ,                      (                                                                                P                    ^                                    CMAX                                ⁡                                  (                  i                  )                                            -                                                                    P                    ^                                    PUCCH                                ⁡                                  (                  i                  )                                                      )                          )              and                              ∑                      c            ≠            j                          ⁢                              w            ⁡                          (              i              )                                ·                                                    P                ^                                            PUSCH                ,                c                                      ⁡                          (              i              )                                          ≤              (                                                            P                ^                            CMAX                        ⁡                          (              i              )                                -                                                    P                ^                            PUCCH                        ⁡                          (              i              )                                -                                                    P                ^                                            PUSCH                ,                j                                      ⁡                          (              i              )                                      )              ,  
When the power of all the PUSCHs without UCI is scaled down to zero, and the total transmit power of the UE still exceeds the maximum transmit power allowed by the UE, then the power of the PUSCH with the UCI is further scaled down. If no PUCCH is transmitted in the current sub-frame i, then {circumflex over (P)}PUCCH(i)=0.
For SRSs transmitted concurrently over multiple carriers in the same sub-frame, if the total transmit power of a UE exceeds the maximum transmit power allowed by the UE, then power of the SRS over each carrier is scaled down with an equal proportion so as to satisfy the limited maximum transmit power allowed by the UE:
                    ∑        c            ⁢                        w          ⁡                      (            i            )                          ·                                            P              ^                                      SRS              ,              c                                ⁡                      (            i            )                                ≤                            P          ^                CMAX            ⁡              (        i        )              ,
Wherein {circumflex over (P)}SRS,c(i) represents a linearity-domain value of PSRS,c(i), and w(i) represents an SRS power scaling down factor over each carrier with 0≦w(i)≦1.
Only intra-band Carrier Aggregation (CA) is supported in uplink transmission defined in the LTE-A Rel-10, and there are assumed similar radio signal propagation characteristics of respective carriers, so all the uplink transmission time are adjusted based upon a Time Advance (TA) obtained in a PRACH procedure over a Primary Component Carrier so that the uplink transmission time of the carriers are aligned and thus power control can be performed in sub-frames.
In the LTE-A Rel-11, uplink CA in different bands (inter-band CA) as well as a mixed deployment CA scheme of a macro base station (denoted by a macro eNB) and a Remote Radio Head (RRH) can be supported. Due to different radio signal propagation characteristics in the different bands and different propagation paths traversed by the macro eNB and the RRH, signals transmitted over different carriers may arrive at the eNB at different time. Thus in the Rel-11, there may be different TAs of different carriers, and uplink transmission time of the carriers may not be aligned, so an uplink channel over a carrier may be transmitted, in different transmission time segments in a sub-frame, concurrently with an uplink channel in a preceding adjacent sub-frame and/or a succeeding adjacent sub-frame. Consequently the power control scheme in sub-frames will not be applicable.